1. Field of the Invention
The present invention relates generally to phase change memories, and in particular to a phase change memory having a more uniform heater and the manufacturing process thereof.
2. Description of the Related Art
Phase change memory devices use phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, for electronic memory application. One type of memory element utilizes a phase change material that may be electrically switched between a generally amorphous structural state and a generally crystalline local-order state or among different detectable states of local order across the entire spectrum between the completely amorphous and the completely crystalline state. The state of the phase change materials is also non-volatile in that, when set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that phase or physical state and the resistance value associated thereto are retained until changed by another programming event. The state is unaffected by removing electrical power.
One problem of this type of memories resides in the fact that, in view of the present manufacturing process, the height of the heater layer varies within a same wafer and from wafer to wafer, thus causing a high level of programming current variation.
This is disadvantageous, since the programmed physical state of the memory cells, and thus the electrical characteristics thereof, depend on the value of the programming current. The variability in the programming current may thus determine errors in storing data, in particular in case of multilevel memories, and thus errors in reading.